A coated membrane is already known from U.S. Pat. No. 3,874,986. This membrane consists of a porous carrier, an ultrathin film of an organopolysiloxane polycarbonate copolymer on the carrier, topped by an ultrathin film, made of polyphenylene oxide. Manufacture is by the "Ward Process," by shaping the polymers on a limited liquid surface. The resultant membrane is suitable for separating gas mixtures, especially mixtures of O.sub.2 and N.sub.2.
Published European Patent Application No. 0,124,028 describes the manufacture of membranes suitable for gas separation, as well as hollow fibers and hollow capillaries. Manufacture is accomplished by deliberate stretching of thermoplastic crystalline polymers shaped by melting, especially polyolefins.
U.S. Pat. No. 4,230,463 describes the manufacture of multicomponent membranes for gas separation. Porous hollow fibers are dipped for this purpose into a dilute or nondilute coating material which may be drawn into the pores by a vacuum inside the porous hollow fiber. Solvents can then be evaporated off if necessary.